These figures, compiled by teacher supply expert John Howson, show that advertisements for headships in the national press were running at a higher level in 1996-97 than at any time since the late 1980s.
The reason for the high turnover, Mr Howson suggests, was the tightening of early retirement arrangements by the last Government, which was announced in the autumn of 1996 and eventually took effect in the summer of 1997. This produced a flood of early retirements of senior staff in late 1996 and early 1997, which had slowed down by last autumn.
Mr Howson, who carried out the survey with help from the National Association of Head Teachers and Secondary Heads Association, points to several reasons for long-term concern. His figures show once again the problem of attracting staff to schools in inner London. More than half of the headships in inner London had to be readvertised, with the problem especially acute in the primary sector; even in outer London and the South-east, the figure was around 30 per cent.
"The London figure is very worrying," said Mr Howson. "It may reveal a wider problem attracting teachers at all levels to work in the capital."
A single readvertisement does not always solve the problem. During early 1997, some schools had to readvertise two or three times for a headteacher and many still had an acting head at the end of the year.
Of the 2.5 per cent of schools that had to readvertise more than once, a quarter were London schools and 40 per cent were church schools. Church schools face growing problems finding active church members as society becomes more secular, Mr Howson says. Roman Catholic schools, nearly half of which had to readvertise, are often quite scattered geographically.
Secondary schools with poor exam results also seem to have greater recruitment problems than others. More than half of 39 secondary schools that had to readvertise and whose GCSE results were available had less than 30 per cent of pupils getting five A to C grades.
The Government has partly recognised the need to pay more to attract heads to low-achieving schools by proposing to drop the pay and conditions requirements for schools in the new education action zones, Mr Howson says. But he adds: "This experiment will still leave too many schools dependent upon market forces and with budgets that do not allow them to offer financial incentives to heads".
Most first appointments to headship have traditionally been of deputy heads between the ages of 35 and 44. But, in the primary sector, only about 7,500 teachers in that age group are deputy heads, producing a ratio of only five deputies for every headship advertised - probably an overstatement, says Mr Howson, since some would not yet be considering further promotion and others would be busy acquiring their headship qualification. He says older teachers should not consider themselves too old for promotion.
In secondary schools, where there are more deputies and fewer headships, there should be less of a problem. But the loss of some 2,500 deputy posts since 1991 - nearly one in four - means there are now fewer than two deputies per head in the secondary sector, and the figure may fall to 1.5 by 2000. This means staff who are not deputies will need to be trained for headship if there are to be enough candidates.